An electro-photographic type image forming apparatus such as a laser printer and an LED printer is known in the prior art. A cartridge is attachable to and detachable from the image forming apparatus. The cartridge is configured to accommodate therein toner.
The number of printable sheets printed by the cartridge is defined as yield information. The image forming apparatus may monitor service life of the cartridge on the basis of the yield information. Such image forming apparatus and cartridge are described in the prior art.